The subject invention concerns the field of rotary encoder switch arrangements in general, and concerns an integrated rotary encoder having a pushbutton switch, in particular.
Many modern electronic instruments utilize discrete rotary encoders to provide front panel control to a user of the various features of the instrument. These discrete rotary encoders may be mounted directly to the rear surface of the front panel, or may be mounted on a printed circuit board (PCB) that is behind, and parallel to, the front panel of the instrument. Such rotary encoders are well known in the art, as evidenced by the wide variety of styles, such as the ECW series manufactured by Bourns, Inc. of Riverside, Calif.
The TDS-7000 series oscilloscopes, manufactured by Tektronix, Inc., Beaverton, Oreg., uses 15 rear-mount rotary encoders on its front panel circuit board. Each of the encoders is mounted to the rear side of the circuit board, such that the actuation shaft passes through the circuit board, and ultimately through a hole in the front panel. While these rotary encoders perform well, it has been found that securing each encoder to the printed circuit board is a labor-intensive time consuming hand operation that entails placing a nut onto a threaded portion of the shaft, tightening it to a specified torque, and hand soldering three electrical leads.
It has also been noted that while each rotary encoder falls within a specified range for operating torque, the variation in torque from encoder to encoder forms a distribution across the range. This variation is largely caused by the fact that discrete rotary encoders are produced at different times by different operators using different machine setups.
The encoders are then placed xe2x80x9con the shelfxe2x80x9d where they are intermixed during the normal sale and supply procedure. Thus, when multiple discrete rotary encoders are used on one PCB, a relatively high torque encoder may happen to be placed adjacent to a relatively low torque encoder. In such a condition, the difference in torque between the two encoders is readily noticeable to a user.
A solution to the variation in torque is to use an integrated rotary encoder, such used in model number 3777S-TEK-010 manufactured by Bourns, Inc., and used in the Tektronix 3000-series oscilloscopes. Such integrated rotary encoders employ a surface mounted encoder module, having an open rear side with exposed electrical contacts that contact printed circuit traces formed on the customer""s printed circuit board (PCB). There are several advantages to this approach. First, the integrated encoders are all assembled at the same time, by the same operator, in the same process. Thus, the unit to unit variation in torque is greatly reduced. Second, in this approach, the integrated encoder manufacturer can provide full service to the customer by fabricating the PCB for the customer, mounting the integrated encoders, and testing the assembly for the customer.
Unfortunately, there are some drawbacks to the use of the above-described integrated encoder. The above-described integrated encoder may have too great a depth in certain applications where it is necessary to place its circuit board in close proximity to a front panel. Also, for applications in which the circuit board is densely populated, a rotary encoder having a large xe2x80x9cfootprintxe2x80x9d, is not a practical solution because a plurality of them will require too much board area.
Co-pending U.S. patent application Ser. No. 09/957,371 entitled REAR MOUNTED INTEGRATED ROTARY ENCODER, (Johnson, et al.) filed Sep. 21, 2001, and co-assigned to Bourns Corporation and to the same assignee as the subject application (i.e., Tektronix, Inc.), discloses an rear-mount integrated rotary encoder which provides a solution to the above noted problems of the prior art.
However, what is needed is a rotary encoder arrangement for use on circuit board mounted in close proximity to a front panel, which exhibits minimal unit to unit variation in torque, and avoids the labor-intensive hand mounting operations described above, and which includes a pushbutton switch feature.
A rear-mount integrated rotary encoder comprises a mechanical portion and a printed circuit board portion. The mechanical portion of a rear mount integrated rotary encoder comprises a housing including a bushing for receiving one end of a rotatable shaft. The rotatable shaft passes through an open front portion of the housing and is mechanically connected to exposed rotatable circuit contacting members. The printed circuit board portion has an encoder contact pattern formed thereon. The printed circuit board has an area larger than the cross sectional area of the housing. The encoder contact pattern surrounds (or is at least concentric with respect to) an aperture in the circuit board. The rotatable shaft of the rotary encoder is passed through the aperture such that the rotatable circuit contacting members contact the encoder contact pattern on the circuit board. An elastomeric button is mounted on the front surface of the circuit board and surrounds the shaft of the rotary encoder to provide a spring-like action. The rotatable shaft is keyed to allow movement orthogonal to the plane of the circuit board while preventing rotation of the knob with respect to the rotatable shaft. When the knob is pressed, the elastomeric button is compressed and a pair of switch contacts, mounted below the elastomeric button, contact each other. In one embodiment, the housing includes projections, substantially orthogonal to the circuit board, for engaging a feature of the circuit board for securing the integrated encoder in an assembled state. In another embodiment of the invention, the housing is attached to the circuit board by means of an adhesive applied to the front surface of the housing. A further feature of the subject rear-mount integrated rotary encoder including a pushbutton switch is that it is substantially cylindrical in shape to reduce the required spacing between adjacent encoders.